add X509Certificate version attribute
diff --git a/docs/hazmat/primitives/interfaces.rst b/docs/hazmat/primitives/interfaces.rst
index 77aa001..d964f25 100644
--- a/docs/hazmat/primitives/interfaces.rst
+++ b/docs/hazmat/primitives/interfaces.rst
@@ -703,6 +703,12 @@
 
     .. versionadded:: 0.7
 
+    .. attribute:: version
+
+        :type: X509Version
+
+        The certificate version as an enumeration.
+
     .. method:: fingerprint(algorithm)
 
         :param algorithm: A